Suspension system, in particular for vehicles capable of cross-country travel

ABSTRACT

A suspension system, in particular for vehicles capable of crosscountry travel, such as tractors or caterpillar vehicles, includes springs connected in series to support the mass to be sprung, in particular the body mass of the vehicle, a coupler mass disposed between said springs, and a locking device operable by a control means to release the coupler mass approximately at one of the oscillation reversal or dead points of the mass to be sprung, in particular the vehicle body mass and to lock it again approximately after half the oscillation of the coupler mass, the springs being designed as hydropneumatic or gas/liquid spring elements, the hydraulic components of which are in fluid connection, the coupler mass being constituted by the liquid column of the hydraulic connection and the locking device comprising a valve arrangement connected in the hydraulic connection to block or open the same.

United States Patent Kauer SUSPENSION SYSTEM, IN PARTICULAR FOR VEHICLESCAPABLE OF CROSS-COUNTRY TRAVEL Inventor: Harald Kauer. Ettlingen.Germany Assignee: Dr. Ludwig Pietzseh. Karlsruhe,

Germany Filed: Sept. 21, I973 Appl. No.: 399,488

Related US. Application Data Primary Examiner.lames B. Marbert [57]ABSTRACT A suspension system. in particular for vehicles capable ofcross-country travel. such as tractors or caterpillar vehicles. includessprings connected in series to support the mass to be sprung. inparticular the body mass of the vehicle. a coupler mass disposed betweensaid springs. and a locking device operable by a control means torelease the coupler mass approximately at one of the oscillationreversal or dead points of the mass to be sprung. in particular thevehicle body mass and to lock it again approximately after half theoscillation of the coupler mass. the springs being designed ashydropneumatic or gas/liquid spring elements. the hydraulic componentsof which are in fluid connection. the coupler mass being constituted bythe liquid column of the hydraulic connection and the locking devicecomprising a valve arrangement connected in the hydraulic connection toblock or open the same.

9 Claims. 9 Drawing Figures Fig. 7 Fig. 2

PATENTEUAPR m 3.876,192

saw 3 o 5 Fig.6

SUSPENSION SYSTEM, IN PARTICULAR FOR VEHICLES CAPABLE OF CROSS-COUNTRYTRAVEL This is a division of application Ser. No. 305,515, filed Nov.10, 1972, now US. Pat. No. 3,799,529.

A vehicle provided with a suspension system, may be regarded as being abody mass supported on the ground through a spring system. If a vehiclecapable of cross country travel, such as a tractor or caterpillarvehicle moves over uneven terrain, the body mass is forced to oscillate,such oscillations depending on the travelling speed of the vehicle andon the height of and distances between the bumps or depressions in theroadway. In the range of the natural frequency of the body mass theamplitudes of the oscillations of the mass may become much greater thanthe height of any bumps or depressions.

The maximum travel of the spring of a vehicle suspension system setslimits for the height of the obstacles which can be taken as well as forthe speed by which the vehicle may move over them.

Usually attempts at reducing the amplitude of the body mass are made byproviding a dampening or shock absorbing means in parallel with thespring. In any such damper part of the oscillation energy of theundampened oscillation is converted into heat, which is dissipated.Increasing dampening on the one hand re duces the oscillation amplitudesof the body mass and, on the other hand, affords poorer suspension.

Any measure taken to reduce the amplitudes of the body mass by dampeningnecessarily leads to a compromise:

the dampening must be so strong that enough energy is dissipated thedampening must be so weak that the effect of the springs is not reducedtoo sharply.

The oscillation energy dissipated by the dampening is at the expense ofthe propulsion energy of the vehicle and thus must be made up for by thedrive means of the vehicle. The amount of energy to be dissipated isquite considerable when the body mass is large. Therefore, the dampersare subject to heavy wear. Finally, even at strong dampening it is notpossible to drive the vehicle in the range of the resonant frequency orthrough said frequency range of the body mass because even the dampenedoscillations are still too strong and no vehicle let alone the driver,can be expected to put up with them. Besides, the dampers are overloadedto such a degree that they will fail after a short time.

For these reasons, it is avoided to drive vehicles suitable forcross-country travel and equipped with the known suspension systemcomprising dampers at a speed in or near the range of resonantoscillations over uneven ground. As the resonant frequency range usuallylies at rather low speeds and even the passing through the resonantfrequency range causes the disadvantages discussed above, travel overuneven terrain so far is possible only at extremely low speeds.

It is an object of the invention to provide for such design of thesuspension system that oscillations of the mass to be sprung by thesuspension system are diminished or extinguished effectively also in theresonant frequency range of the mass to be sprung.

It is a further important object of the invention to provide for suchdesign of the suspension system that oscillations of the mass to besprung are diminished or extinguished without dissipation of energy.

Another object of the invention is to provide a suspension system forvehicles suitable for cross-country travel permitting the vehicleequipped with such suspension system, e.g. a tractor or caterpillarvehicle to be driven over uneven terrain at higher speed and even in theresonant frequency range and beyond, the unevenness of the ground to betaken by the vehicle reaching up to the dimensions of the maximum pathof the spring.

A suspension system according to the invention comprises springsconnected in series to support the mass to be sprung, a coupler massdisposed between the springs, and a locking device operable by a controlmeans to release the coupler mass approximately at one of theoscillation reversal or dead points of the mass to be sprung, inparticular the vehicle body mass, and to lock it again approximatelyafter half an oscillation of the coupler mass, the springs beingdesigned as hydropneumatic spring elements, the hydraulic components ofwhich are in fluid connection, the coupler mass being constituted by theliquid column of the hydraulic connection, and the locking devicecomprising a valve arrangement connected in the hydraulic connection toblock or open the same. With such a suspension system oscillatingmovements of the mass to be sprung are largely avoided even if it isexcited to oscillate in its resonant frequency range. The oscillatingcondition of the mass to be sprung may be determined by measuring theforce and/or time, path, speed, accel eration.

A suspension system according to the invention used for suspension of avehicle operates as follows:

When the vehicle is stopped, the locking device is released. As soon asthe vehicle starts moving the locking device locks the coupler mass withrespect to the body mass at a slight deflection of the body massalready. The locking device then stores the spring energy of the lockedspring, while the other spring remains fully effective.

When the vehicle moves over uneven terrain, the body mass and thecoupler mass connected with the same remain at rest as long as theunevenness is slight and the speed high. However, if that is not thecase, the body mass is forced to oscillate about the static equilibriumposition of the system and the amplitude and direction of theoscillations are detected by the control means, for instance, in theform of the oscillating speed.

The control means realeases the locking device at a change of thedirection of the speed (dead or reversal point of the oscillation of thebody mass). Due to the spring energy released by the locking device thecoupler mass then begins to oscillate at its natural frequency with aninitial deflection with respect to its static equilibrium position. Thelocking device is closed after half the oscillation period of thecoupler mass, i.e, at a time at which the coupler mass is located at theop posite dead or reversal point of its oscillation. Hereby anotheramount of energy in the form of spring energy is stored in the lockingdevice. This energy, however, is of opposed effect (sign) as compared tothe previously stored amount of energy. The locking device remainsclosed until the control means again reports reversal of the oscillatingmovement of the body mass. Then the switching cycle starts again.

Thus stored energy is supplied to the suspension system of the inventionat suitable times (lock release) and is again withdrawn from the sameafter a very short time (half the oscillation period of the small mass)and at opposed sign. This prevents oscillations of the body mass ofgreat amplitude. The body mass merely oscillates at small amplitudes andat frequencies corresponding approximately to those of the coupler mass.Since the locking device is controlled by way of the oscillatingcondition, e.g., the oscillating speed of the body mass, extinction orat least diminuation of the oscillations may be obtained at any excitingfrequencies without any dissipation of energy by dampening.

It is a further object of the invention to provide a simplifiedsuspension system suited in particular for the effective diminishing orextinction of oscillations of a vehicle seat caused to oscillate whenthe vehicle moves over rough ground.

Therefore, a suspension system according to the invention comprisessprings connected in series to support the mass to be sprung. inparticular the seat of the vehicle, a coupler mass disposed between saidsprings, and a locking device operable by a control means to re leasethe coupler mass approximately at one of the oscillation reversal ordead points of the mass to be sprung, in particular the mass of the seatand to lock the same again approximately after half an oscillation ofthe coupler mass, the locking device comprising two ratchet meanscapable of being switched and acting in opposed sense to selectivelycooperate with the coupler mass between two springs, in particularhelical springs, connected in series, the first ratchet means beingdesigned to block movement of the coupler mass in the one effectivedirection of the springs and the second ratched means to block movementin the opposite ef fective direction.

Fundamentally. this suspension system operates as the one describedabove. It is simplified in that the locking after half an oscillation ofthe coupler mass may be effected automatically by the utilization of theunidirectional ratchet means without the need for any locking signal tobe supplied by the control means. Thus there is no need to measure thevery brief half oscillation period of the coupler mass, transmit acontrol signal, and effect the locking process within the short' estpossible time of response. That is technically complicated but neededwith the suspension system first described.

A useful control means for all the suspension systems specifiedcomprises measuring means for detecting the pitching oscillations andthe lifting oscillations to transmit the signals for actuation of thelocking device, pref erably at or near zero of the pitching and/orlifting speed curve through the zero line marking the time. Separatemeasuring means may be provided for the pitching oscillations and forthe lifting oscillations. In a first embodiment they comprise agyroscope for detecting the pitching oscillating speed mounted at thepitching pivot point of the vehicle body and of an acceleration sensorwith an integrator connected to the output thereof to detect the liftingoscillating speed. The separate measuring of the pitching and liftingoscillating speeds requires provision of two separate control channelswhich are reversed automatically in dependence on the relationshipbetween lifting and pitching speed. In that case only one type ofoscillations each is attackable. This first embodiment of the controlmeans thus does not permit the simultaneous diminuation or extinction oflifting and pitching oscillations. in practice, however, lifting andpitching oscillations, are superposed in time. Therefore, a preferredsecond embodiment of the control means for joint and simultaneous attackof both kinds of oscillations provides as measuring means for detectingthe pitching oscillations and the lifting oscillations of the body masstwo acceleration sensors, with integrators connected to the outputthereof, one being disposed at the front end in the travelling directionand the other one at the rear end of the mass in particular the vehiclebody.

Conveniently the output signals proportional to the oscillating speedsfurnished by the acceleration sensors formed of the acceleration sensorswith the integrators, are combined according to the function v, k-vwherein k is a constant, and the switching signal for the locking deviceis always emitted as this function passesthrough zero.

A preferred value for the constant k is 2.

The invention will be described further by way of example, withreference to the accompanying drawings, in which:

FIG. 1 illustrates a diagrammatic layout of a first embodiment of asuspension system according to the invention,

FIG. 2 illustrates a diagrammatic layout of a modified suspension systemaccording to the invention,

FIG. 3 illustrates a modified embodiment of the suspension systemaccording to the invention,

FIG. 4 illustrates a diagrammatic embodiment of a valve arrangementconveniently used in the suspension system of the invention,

FIG. 5 illustrates a cross sectional elevation of a nonreturn valvepreferably used with the invention,

FIG. 6 illustrates three coordinated graphs in each of which a givenroadway profile and the corresponding deflections of the body masscaused by the same as well as the coupler mass are plotted withreference to time, to demonstrate the mode of operation of thesuspension system according to FlGS. l, 2 or 3,

FIG. 7 illustrates a diagrammatical layout of a third embodiment of asuspension system according to the invention,

FIG. 8 illustrates two graphs of the course of the pitching speed andlifting speed, respectively, with reference to time approximately at thepitching pivot point of the vehicle, including a vehicle diagram with afirst measuring arrangement according to the invention,

FIG. 9 illustrates three graphs of courses of oscillating speeds withreference to time, the two top graphs illustrating the combinedpitching-lifting-oscillatingspeed at the front and rear ends of thevehicle and the lower graph illustrating a course combined according toa given function of the two upper speeds, including a vehicle diagramwith a second preferred measuring arrangement according to theinvention.

The suspension system according to FIG. 1 is arranged between the body201 and the wheel 202 of a vehicle capable of driving over roughterrain. An hydraulic cylinder 203 of the suspension system is mountedon the body of the vehicle, and the piston 204 of the cylinder 203 ispivoted at the support of the wheel 202.

The pressure chamber 205 of the hydraulic cylinder communicates throughconduits 206 and 207 with liquid spaces 208 and 209, respectively, ofaccumulators 210 and 21], gas spaces 212 and 213, respectively,

which are separated from the liquid spaces 208 and 219 by means offlexible diaphragms 214 and 215, respectively. A valve arrangement 216is provided in the pressure chamber 215. This valve arrangementcomprises two non-return valves which can be opened, act in oppositedirections, and are capable of being controlled individually. The valvearrangement 216 is actuated by a sensor measuring the oscillating speedof the body 210.

The suspension system shown in FIG. I operates as follows: When thevehicle is stopped, both non-return valves of the valve arrangement 216are open so that the accumulator spaces 208 and 209 communicate witheach other. As the vehicle starts to move, the valve arrangement 216 isclosed even at minor deflection of the body mass 201, i.e., bothnon-return valves are closed. Thus only the accumulator 211 acts as anhydropneumatic spring element, whereas the spring energy of theaccumulator 210 is stored by means of the valve arrangement.

When the vehicle moves over an uneven roadway, the body mass 201 iscaused to oscillate or swing about the static equilibrium position ofthe system. The sensor senses the amplitude and direction of theseoscillations as oscillating speed.

The sensor opens either one of the non-return valves of the valvecombination 216 in dependence on the direction of the oscillating speedas soon as the oscillating speed reaches zero. Thereupon the releasedspring energy of the accumulator 210 causes the column of hydraulic oilto begin to oscillate at natural frequency in the cylinder 205 andconduits 206 and 207 with an initial deflection with respect to itsstatic equilibrium position. After one-half of the oscillation time ofthe liquid column. in other words, at a time at which the liquid columnis at its opposed point of return of the oscillation, the liquid whichnow begins to flow back closes the previously opened non-return valve ofthe valve combination 216. Hereby again an amount of energy in the formof spring energy is stored in the accumulator 210. This time, however,the stored energy has the opposed effect (reversed sign) of the energystored previously. The valve combination 216 remains closed until thesensor again signals a change of sign of the speed of the body mass.Then a new switching cycle begins by opening of that non-return valve ofthe valve combination 216 which is determined by the direction of thespeed.

The mode of operation of the suspension system is illustrated in FIG. 6.

The three graphs shown in FIG. 6 which deflections are plotted withreference to time I are coordinated with each other in verticaldirection. The lowest one illustrates an desired predetermined roadwayprofile 140 which is shown by way of example with periodic changes. Thegraph above illustrates the deflections 141 of the coupler mass formedby the liquid column in the cylinder 205 and the conduits 206, 207 asresulting from the changing profile and the upper graph illustrates thedeflections 142 of the body mass 201.

The points marked 1 to 9 in the deflection curves 141 and 142 indicatethe times at which the locking is released. At each of these times thedeflection speed of the body mass becomes zero.

Points 1 to 9 characterize those points in the deflection curve 141 atwhich the locking device is locked gain after half an oscillation eachof the coupler mass.

Between each two times 1 and 2, 2 and 3, 3 and 4, and so on, the couplermass consequently is rigidly connected with the body mass so that itswings in synchronism with the same and at the same deflection.

It is evident from FIG. 6 that the body mass is kept almost at rest inspite of great unevenness in the roadway.

In the suspension system shown in FIG. 1 shock absorbing means whichdissipate considerable amounts of energy at greater body oscillationsare eliminated. Despite that it is possible for a vehicle equipped witha suspension system as shown in FIG. 1 to move at any desired speed overuneven terrain the size of the bumps and depressions corresponding inextreme cases approximately to the permissible travel of the spring,without amplifying the oscillations of the body mass such that theamplitude would no longer be permissible. This also applies tooscillations within the range of the natural frequency of the body mass.

In FIGS. 1 and 2 like parts are designated by the same referencenumerals and, inasmuch as the embodiments are alike, the structure andoperation of the embodiment shown in FIG. 2 is not described again.Other than with the embodiment according to FIG. 1, which comprises avalve arrangement, the pressure chamber as shown in FIG. 2 is providedwith a freely floating piston 217. The freely floating piston is lockedand released in the cylinder by a locking device (not shown) in the samerhythm as the valve arrangement in the embodiment of FIG. 1.

FIG. 3 shows a particularly advantageous embodiment of the invention.With this embodiment the wheel 202 of the vehicle subjected to a forcein the direction of the arrow A is supported at one end of a support arm220, the other end of which is attached to the center of a link 221which in turn is connected by an axle 219 to the body (not shown). Apiston each 222 and 223 is pivoted at the free ends of the link 221. Thepistons 222 and 223 operate in hydraulic cylinders 224 and 225,respectively. The pressure chambers 226 and 227 of the cylinders 224 and225, respectively, communicate with liquid spaces 228 and 229 ofaccumulators 230 and 231, respectively. The accumulators 230 and 231each comprise a gas space 232 and 233, separated by flexible diaphragms234 and 235, respectively, from the liquid spaces 228 and 229,respectively. The pressure spaces 226 and 227 of the two cylinders 224and 225 communicate through a conduit 236. This arrangement plus thefact that the pistons act in opposed sense provides a series arrangementof the two hydropneumatic spring elements.

The suspension system of FIG. 3 as described thus far corresponds to aconventional suspension system. It is merely supplemented by a valvecombination 237 (FIG. 4) connected in the conduit 236 through which thetwo liquid spaces 228 and 229 communicate. The two accumulators whichalso the convention suspension system comprises, are so much larger herethat one spring will have the same spring rate as the two springsconnected in series in the conventional suspension system. As the body(not shown) oscillates, the valve arrangement is actuated in the samerhythm as the suspension systems according to FIG. 1 or 2.

At normal driving conditions of the vehicle the valves of the valvearrangement 237 are open. The spring characteristic is identical to thatof the conventional suspension system. However, apart from any possiblethrottling in the conduit 236 connecting the two accu mulators 231 and230, the suspension system is operated without any dampening.

When oscillations of the vehicle occur, the nonreturn valves of thevalve arrangement 237 are closed at the time of maximum deflection ineither direction so as to shut-off the accumulator 231, thereby storingspring energy in the accumulator 231. The body mass (not shown) is thenmoved back into the static equilib rium position by the accumulator 230which is still active. At this position the angular pitching speed ofthe body mass has become zero. At this time one nonreturn valve isopened and the biased amount of liquid, e.g., oil in the accumulator 231is accelerated.

It flows very quickly into the accumulator 230 to bias the same. As theoil swings back from the accumulator 230 into the accumulator 231, theother non-return valve is closed so that the accumulator 230 remainsloaded and the accumulator 231 remains closed in discharged condition.If an obstacle in the roadway then tends to move the body mass (notshown) upwardly, the active accumulator 230 must be discharged again soas to counteract the movement of the body. To this end the othernon-return valve is opened and the oil of the active, loaded accumulator230 flows into the empty accumulator 231 to bias the same. At the timeat which the oil wants to flow back into the accumulator 230, the onenonreturn valve of the valve arrangement 237 is closed. The cycle isrepeated in reverse direction if the mass of the vehicle tends to movedownwardly.

Thus stored energy is supplied to the suspension system according to theinvention (opening of the valve) at suitable times and is withdrawnagain from the same with reversed sign after a very short interval (halfof the oscillation of the oil between the two accumulators).

FIG. 4 shows a diagram of a valve arrangement preferably used with theembodiments according to FIGS. 1 and 3. The valve combination comprisestwo nonreturn valves 250 and 251 capable of being opened and eachpermitting flow in one direction only. Valve 250 permits flow from theinlet 252 to the outlet 253 when control line S] is actuated. Returnflow from the outlet 253 to the inlet 252 is not possible until thecontrol line 52 of the valve 251 is actuated. The sensor which detectsthe oscillating speed of the body mass controls either valve 250 or 251in dependence on the direction of the speed.

FIG. 5 is a diagrammatic representation of a non return valve capable ofbeing opened. This valve is preferably used as valve 250 and 251 in thevalve ar rangement according to FIG. 4. The valve has an inlet passage240 and an outlet passage 241. The two passages 240 and 241 ofrelatively large cross sectional area communicate through a valvechamber 242 when the valve is open. The valve chamber 242 houses thevalve member 243, the mass of which is relatively small. The hydraulicpressure acting in the pressure chamber 205 or 226 and 227 urges thevalve member 243 generally away from the openings of the passages 240and 241 in the valve chamber 242. A passage 244 is located at the sideof the valve chamber 242 opposite the openings of the passages 240 and241, and the valve member may be subjected to high pressure through thispassage. Under the action of this high pressure the valve member 243briefly enters into sealing engagement with the opening 241 in the valvechamber 242.

This interrupts the flow between the passages 240 and 241 so that onlyone accumulator each will be operating. As the oil flows back from thepassage 241 to the passage 240, the valve member 243 is forced, byreason of its geometry, to enter quickly into sealing engagement withthe opening of the passage 240 so that the valve is blocked uponreversal of the direction of flow. The valve shown in FIG. 5 may alsoreplace the valve arrangement of FIG. 4, provided it operates atsufficient actuating speed, and it may be installed directly as valvearrangement" 216 or 237 in the suspension system according to FIG. 1 or3, respectively.

The sensor may be embodied by a reversing gyroscope fastened at thevehicle. It senses the pitching oscillations of the vehicle and actuatesthe quick-acting valve in the rhythm defined above.

The embodiment of FIG. 7 shows the seat 301 of a vehicle pivoted at thevehicle body by means ofa parallel linkage 302 designed for easypivoting motion. The seat 301 is cushioned by two springs 304 and 305connected in series. Two ratchet and pawl means 307 and 308 are mountedon a link 306 between the two springs 304 and 305. The pawls 309, 310 ofthese ratchet means 307, 308 are supported at the vehicle body andinterconnected by a connecting bar 311. A friction pad 312 is arrangedso as to be pressed against a friction surface at the drivers seat.Movement of the friction pad is transmitted to the connecting bar 311 bya shifting rod 313 and a toggle link 314. Movement of the friction pad312 into pressure contact is caused by a coupling device 320 by means ofa servo force. The coupling device 320 receives its switching signalsfrom an acceleration sensor (not shown) mounted at the seat 301 andprovided at its output side with an integrator. The acceleration sensormeasures the absolute speed of hte seat 301, i.e., its speed relative tothe stationary underground and emits a switching signal when the abso'lute speed of the seat motion approaches or reaches zero.

FIG. 7 shows the driver's seat 301 in equilibrium position at which anyrelative movement of the seat 301 with respect to the vehicle body 303is cushioned only by the spring 304 because the spring 305 is lockedagainst compression by the pawl 309 of the unidirectional ratchet means307. Upon oscillating movement of the seat 301 the friction pad 312 ispressed against the seat in response to the switching signals emitted bythe acceleration sensor, thus following further movement of the seattogether with the linkage assembly 311, 313, 314. Since this disengagesthe pawl 309, the spring 305 is released so that the link 306 may swingtowards the vehicle body 303, at the same time compressing the spring305. Simultaneously, i.e., as the pawl 309 of the ratchet means 307 isdisengaged, the pawl 310 of the ratchet means 308 is engaged. This doesnot obstruct the oscillating movement of the two springs 304, 305towards the vehicle body 303. Yet the pawl prevents the link 306 fromreversing its direction of movement so that after half an oscillationthe link is again locked and energy is stored in the spring 305. In thisrespect the present embodiment does not differ from those describedpreviously. The difference resides in the fact that the locking processis effected without the aid of control means. In other words, there isno need for measuring the very brief period of one half of theoscillation of the link and then emitting a switching signal, asrequired with the other embodiments, a requirement which can be realizedat considerable expense only. The ratchet means 307, 308 may be replacedby any commercially available one-way clutch devices, such asoverrunning clutches with roller members or cam members which are ofsimple structure and have proved very successful in practice.

At the top of FIG. 8 a tractor is shown diagrammatically which may pitchat the angle a about the pitching pivot point M. The body mass A iscaused to make such angular pitching movements in the form ofoscillations when the vehicle travels over rough ground. The vehicle isfurther caused to carry out oscillating lifting movements. The course vof the speed of the pitching movements and the course v of the speed ofthe lifting movements are plotted in the two graphs of FIG. 8.

A gyroscope WK is disposed approximately at the pitching pivot point Mto sense the pitching speed 1/ The lifting oscillation speed v is sensedby an accelerator sensor B,- which is connected with its output to anintegrator (not shown) to determine the lifting oscillating speed v Aswitch-over device, likewise not shown, renders either the gyroscope WKor the acceleration sensor B active so that either of them will emitswitching signals for actuating the locking device. These switchingsignals are always emitted as the respective speeds become approximatelyzero.

The swith-over device is of such design that it will keep the gyroscopeWK actuated up to a predetermined minimum pitching oscillating speed,that it will switch off the gyroscope WK below said minimum pitchingspeed and switch on the acceleration sensor B and that it will againswitch off the acceleration sensor B and switch on the gyroscope WK uponfailure to reach a minimum lifting speed.

The graphs of FIG. 9 relate to the acceleration sensor arrangement asshown in the diagram of the tractor at the top of FIG. 9. The body massA is provided at the front end in the direction of travel with anacceleration sensor B, and at the rear end with another accelerationsensor B An integrator each (not shown) is connected to the output ofthe acceleration sensor. Therefore, as a whole the oscillating speeds v,and v are detected. These oscillating speeds are composed of the liftingspeeds and pitching speeds. The speeds v and v are plotted in the uppertwo graphs of FIG. 9. For comparison the two graphs further show indashed lines the respective pitching oscilating speeds VH2 and v,, whichcould only be detected by separate gyroscopes not shown.

The dashed-line pitching speeds and the continuousline speeds composedof lifting and pitching speeds v and v are combined in the lowest graphof FIG. 9 according to the relationship: v, k v It can be seen in thisgraph that the passing points of the curve v, k v through the zero lineare shifted as compared to the respective points for the dashed-linecurve of the pure pitching speed which always remain at the same placeand thus also correspond to the respective points in the top graphs ofFIG. 8. This shift is needed in order to be able to cover both thepitching speed and the lifting speed.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A suspension system for suspending the body mass of a vehicle capableof cross-country travel, such as tractors or caterpillar vehicles withrespect to ground, comprising: springs connected in series to supportthe body mass, a coupler mass disposed between said springs, controlmeans, a locking device operable by said control means to release thecoupler mass at a predetermined point of the swinging motion of thecoupler mass, said control means comprising measuring means fordetecting the pitching oscillations and the lifting oscillations of thebody mass and for producing the signals for actuating the lockingdevice.

2. A suspension system according to claim 1, wherein the coupler mass isreleased approximately at one of the oscillation reversal or dead pointsof the body mass and is locked again after half an oscillation of thecoupler mass.

3. A suspension system as claimed in claim 1, wherein the measuringmeans is effective to emit sig nals for actuation of the locking deviceapproximately at zero pitching and/or lifting speed of the body mass.

4. A suspension system as claimed in claim 1, wherein the measuringmeans are constructed and arranged for detecting the pitchingoscillations and the lifting oscillations and includes a gyroscopemeasuring the change speed of the pitch angle of the body massapproximately at the pitching pivot and an acceleration sensor with anintegrator connected to the output to convert the output signals of theacceleration sensor into signals proportional to the speed of thepitching oscillating movement.

5. A suspension system as claimed in claim 4, and a switch-over devicefor selective activation of the gyroscope or the acceleration sensor toestablish that the gyroscope alone is operative up to a minimum speed ofthe change in pitch angle, that upon failure to reach said minimum speedthe gyroscope is switched off and the acceleration sensor is witched in,and that upon failure to reach a minimum speed of the liftingoscillating movement the acceleration sensor is switched off and thegyroscope is again switched on.

6. A suspension system as claimed in claim 1, wherein the measuringmeans for detecting the pitching oscillations and the liftingoscillations of the body mass comprises two acceleration sensors havingintegrators connected to their outputs, one thereof being arranged atthe front end in the direction of travel of the vehicle and the otherone at the rear end of the vehicle body.

7. A suspension system as claimed in claim 6, wherein said measuringmeans is effective to establish output signals v and v proportional tothe speeds ascertained by the measuring means, the measuring meansincluding two sets of an acceleration sensor and an integrator connectedto said output signal and combined according to the function v k vwherein k is a constant, and in that the switching signal for thelocking device is always emitted when this function becomes zero.

8. A suspension system as claimed in claim 6, wherein the constant kapproximately has the value 2.

9. A suspension system as claimed in claim 1, wherein said springscomprise gas/liquid spring elements the hydraulic components of whichare in fluid connection, the coupler mass being constituted by theliquid column of the hydraulic connection, and the locking devicecomprising a valve arrangement connected in the hydraulic connection toblock or open the same.

1. A suspension system for suspending the body mass of a vehicle capableof cross-country travel, such as tractors or caterpillar vehicles withrespect to ground, comprising: springs connected in series to supportthe body mass, a coupler mass disposed between said springs, controlmeans, a locking device operable by said control means to release thecoupler mass at a predetermined point of the swinging motion of thecoupler mass, said control means comprising measuring means fordetecting the pitching oscillations and the lifting oscillations of thebody mass and for producing the signals for actuating the lockingdevice.
 2. A suspension system according to claim 1, wherein the couplermass is released approximately at one of the oscillation reversal ordead points of the body mass and is locked again after half anoscillation of the coupler mass.
 3. A suspension system as claimed inclaim 1, wherein the measuring means is effective to emit signals foractuation of the locking device approximately at zero pitching and/orlifting speed of the body mass.
 4. A suspension system as claimed inclaim 1, wherein the measuring means are constructed and arranged fordetecting the pitching oscillations and the lifting oscillations andincludes a gyroscope measuring the change speed of the pitch angle ofthe body mass approximately at the pitching pivot and an accelerationsensor with an integrator connected to the output to convert the outputsignals of the acceleration sensor into signals proportional to thespeed of the pitching oscillating movement.
 5. A suspension system asclaimed in claim 4, and a switch-over device for selective activation ofthe gyroscope or the acceleration sensor to establish that the gyroscopealone is operative up to a minimum speed of the change in pitch angle,that upon failure to reach said minimum speed the gyroscope is switchedoff and the acceleration sensor is witched in, and that upon failure toreach a minimum speed of the lifting oscillating movement theacceleration sensor is switched off and the gyroscope is again switchedon.
 6. A suspension system as claimed in claim 1, wherein the measuringmeans for detecting the pitching oscillations and the liftingoscillations of the body mass comprises two acceleration sensors havingintegrators connected to their outputs, one thereof being arranged atthe front end in the direction of travel of the vehicle and the otherone at the rear end of the vehicle body.
 7. A suspension system asclaimed in claim 6, wherein said measuring means is effective toestablish output signals v.sub.1 and v.sub.2 proportional to the speedsascertained by the measuring means, the measuring means including twosets of an acceleration sensor and an integrator connected to saidoutput signal and combined according to the function v.sub.1 - k .sup..v.sub.2, wherein k is a constant, and in that the switching signal forthe locking device is always emitted when this function becomes zero. 8.A suspension system as claimed in claim 6, wherein the constant kapproximately has the value
 2. 9. A suspension system as claimed inclaim 1, wherein said springs comprise gas/liquid spring elements thehydraulic components of which are in fluid connection, the coupler massbeing constituted by the liquid column of the hydraulic connection, andthe locking device comprising a valve arrangement connected in thehydraulic connection to block or open the same.